The production of viscous hydrocarbons and bitumen from tar sands, is not readily achieved without some form of production enhancement. Among the most widely utilized of the enhancement steps is to thermally treat the productive layer thereby to encourage the rate of production. This form of enhancement normally constitutes the introduction of a heating medium, usually hot water or steam, directly into the substrate.
The effects of this introduction of pressurized heating medium is two-fold. Firstly the elevated temperature heats the hydrocarbon product to increase its mobility, or stated otherwise, to decrease its viscosity. Secondly, the presence of the pressurized heating media within a substrate tends to force the movable hydrocarbon toward a lower pressure zone. The latter is normally established by the positioning of a producing well, in such a location within the substrate as to receive the pressurized flow.
In one of the most commonly practiced methods of this enhanced recovery procedure, pressurized steam, functioning as the heating medium is introduced or flooded into a single well whereby to be discharged through perforations in the latter and into the substrate. The heated and flowable hydrocarbon emulsion is caused to move toward the producing well.
Rather than producing from a remotely positioned well, the huff and puff method can be utilized. In the latter, a single well is provided with a heating medium such as steam, to establish a heated environment. Thereafter the well is closed in to permit the heat to penetrate into a wider area of the substrate. Subsequently, the well is activated to produce the now flowable hydrocarbon or bitumen therefrom.
In any steam flood or thermally stimulated operation, because the steam enters at a high temperature and under substantial pressure there will be a natural propensity for it to rise through the earthen productive layer. The rate of rise will depend on the composition of the substrate and on the length of time to which it is subjected to the pressurized injection of heating medium.
In either event, the heating medium will eventually cause the hydrocarbon flow to break through the substrate and into a producing well. Logically, the heating medium will tend to follow the path of least resistance through the substrate. Thus, it will establish the necessary heating step which gradually liquefies the retained bitumen or viscous petroleum.
The composition of the substrate will be a major factor in determining the effect of the injected steam and its passage through the productive layer. As noted, the steam will tend to rise through the productive layer while contacting the viscous hydrocarbon.
Over a period of time, this continued pressurized introduction of heating medium will cause the steam to override a portion of the hydrocarbon containing layer and move directly to the producing well. The result of such action is that a considerable portion of the productive layer is completely bypassed. The hydrocarbon held therein will remain unheated and in place since its condition is not affected by the steam.
Toward overcoming or obviating this presence of an unproductive hydrocarbon layer in the midst of a highly productive area, the present method is disclosed. Specifically, the function of the heating and stimulating medium is maximized by introducing it directionally into a limited area. Thus, a substantially vertical subsection of the substrate layer is segreated by a series of wells which tend to marginate said subsection. These wells are comprised of at least two horizontally spaced and vertically disposed wells. In addition, one third well is positioned to extend in a substantially horizontal direction passing adjacent to the bottoms of the respective vertical wells.
By the controlled introduction of the heating medium, such as steam into two of these wells, a thermal front can be established in the segregated subsection. This front, by virtue of the pressurized heating medium, is caused to advance laterally through the productive layer.
It is therefore an object of the invention to provide an enhanced recovery technique for producing viscous hydrocarbon products which must first be put into flowable condition before being produced. Another object is to provide a method for producing viscous hydrocarbons or bitumen from a tar sand formation by the controlled introduction of a heating medium into the productive layer. Still another object of the invention is to provide a method for producing viscous hydrocarbon products from a subterranean layer by establishing a thermal front within the layer which advances horizontally toward a producing well.